Electrodes are widely used in the biomedical environment. They can be used for electrically stimulating a patient and/or monitoring of electrical signals of the patient. Generally, electrodes are applied on human beings, although they can be used on other mammals, such as dogs, cats, horses, and the like. A mammalian body generates many different electrical signals. The monitoring of these signals can provide valuable diagnostic information for the medical practitioner on the physiological functions of the patient generating the signals. Electromyograms (EMG), electrocardiograms (ECG) and electroencephalograms (EEG) are examples of records of commonly monitored electrical physiological signals. In addition, sometimes it is necessary to stimulate an individual to promote physiological activity. For example, muscle groups may need to be stimulated. In some patients, the rhythm of the heart may have to be controlled by a pacemaker. In other patients, there may be a tendency to undergo cardiac fibrillation, in which case prompt defibrillation by controlled electrical shocks to the heart is critical for the survival of the patient.
To obtain effective electrical connection between an electrode and the surface of a mammalian body, it is necessary to establish good contact between the electrode and the surface. For example, in the monitoring of an ECG, the electrode is attached to the skin by means of an electrically conductive adhesive. Alternatively, an electrically conductive paste, cream, or gel is disposed between the skin and the surface of the electrode. In such a case, the electrode may have to be secured in place by adhesive tape or the like.
An electrode suitable for monitoring physiological signals or stimulating physiological activities typically contains an electrically nonconductive layer (or substrate) and an electrically conductive layer disposed on the substrate.
A relatively expensive metal is often used for signal sensing or electrical current dispersion and is sandwiched or interposed between the nonconductive substrate and the conductive adhesive. After an electrode has been used, it often must be disposed of or discarded. Even in the case of reusable electrodes, after a period of use, an electrode may become functionally impaired and is no longer useable. Disposal of such electrodes without recycling represents a loss of a material that has significant economic value. Furthermore, the disposal of such electrodes, which may contain metals such as silver, copper, and the like, often results in pollution. Metals such as copper and silver, if not properly disposed of, may leach out of the electrodes and contaminate the environment. Therefore, it is preferable that the electrodes be recyclable, i.e., the metals be reclaimable from the electrodes after the electrodes are used.
In conventional electrodes, an electrically conductive material, usually a metal, is bonded to an electrically nonconductive material, usually a water-insoluble polymeric material. Any effort to recycle the electrode faces the problem of economically separating the metal from the polymeric material.
Cartmell (U.S. Pat. No. 4,674,511) discloses a medical electrode which may be x-ray transparent. The medical electrode contains a thin layer of a conductive paint adhered to a thin supporting substrate. A first area of the conductive material is adapted for contacting an electrolyte used to bridge the conductive material to the skin. A second area of the conductive material is provided for connection of an electrode to external equipment. A silver paint is described as preferably applied by silk-screening. Conductive adhesives are also described to be applicable over the conductive layer.
Monter, et al. (U.S. Pat. No. 3,976,055) disclose an electrode for monitoring signals such as electrocardiographic signals. The electrode has a conductor containing a first galvanically inactive material and a second galvanically active conductive material. The first conductive material may contain a plastic body formed from a nonconductive binder made conductive by inclusion of electrically conductive carbon disbursed therein. Metallic particles may also be incorporated into the electrode to improve performance.
Berg (U.S. Pat. No. 4,066,078) discloses a disposable electrode for use in medical applications including monitoring and stimulation. The electrode contains a conductive member which may be a pliable sheet of material. A material having adhesive properties is provided to assist the adherence of the electrode to the skin. Suitable electrically conductive organic polymers for providing an adhesive composition are also disclosed.
Larimore, et al. (U.S. Pat. No. 4,352,359) disclose a disposable biomedical electrode. The biomedical electrode contains an electrically conductive material on the body-contacting surface. The electrically conductive material has a dermally non-irritating, conformable, cohesive, synthetic, hydrophilic polymer. In one preferred embodiment, an electrical connector stud extends from an electrode plate which is in contact with the conductive material. The polymeric material in the conductive material has at least five or more percent of monomer units containing a salt of a carboxylic acid. The possibility of electrodes containing electroplates of silver or nickel are disclosed.
Gadsby et al. (U.S. Pat. No. 4,852,571) disclose a disposable, biopotential electrode having a plastic base, a layer of carbon, a layer of silver-silver chloride and an electrically conductive adhesive.